(1) Field of the Invention
The invention relates to pressure vessels, and is directed more particularly to an insert which fills an opening in a wall of such a vessel, frames a smaller aperture, and serves as a mounting for an aperture closure member, such as a hatch or acoustical device.
(2) Description of the Prior Art
The United States Navy originally developed a deep diving shell in the warhead section of a practice torpedo. Such shells typically contain transducers and recorders which provide a record as to the performance of a torpedo in a trial or test, such as a simulated attack, or the like.
The shell is cylindrically-shaped and is provided with a layered wall having a core of an aluminum honeycomb structure, bounded by inboard and outboard composite skins of glass fiber reinforced epoxy. The honeycomb core is about 1.1 inch thick and the composite skins are each about 0.1 inch thick. When it is desired to provide an opening in the shell wall for access or for mounting of a transducer, or the like, it is necessary to provide a frame having an aperture therein and having means for supporting an access hatch, or an instrument, and for providing strength to the aperture defined thereby. The honeycomb shell wall structure lacks the strength to support an aperture therein. Accordingly, an insert typically is provided for filling the opening in the shell wall, the insert having sufficient strength to support an aperture therein and a selected closure member.
The inserts used heretofore have generally been of aluminum. When aluminum inserts are used with shells having wall skins of glass-epoxy composites, the modulus of elasticity of the insert exceeds the modulus of elasticity of the wall skins by over 400% in a direction through the thickness of the skins. Failures have resulted from the mismatch of moduli of elasticity. A problem that one encounters in attempting to correct such imbalance, is the fact that the shell skins have widely varying moduli of elasticity in directions through the thickness, longitudinally, and through the "hoop", that is, through the curve of the wall skin. It has been found difficult to provide an insert having a modulus of elasticity substantially equal to the shell skin moduli in all three directions.
Thus, there is a need for an insert having a modulus of elasticity similar to the "through the thickness" modulus of elasticity of the shell wall skins and relatively close to the transverse, or "hoop", and longitudinal moduli of elasticity of the shell wall skins.
Inserts are also necessary in conventional pressure vessels containing a pressurized gas or fluid. The one difference is that the pressurized environment is on the interior of the pressure vessel wall. Similar problems occur with openings in these walls.